Advanced silicon-based materials and devices using chemical vapor deposition

Novel silicon-based materials (a-Si, poly-Si, SiGe) based on chemical vapor deposition have been used to fabricate poly-Si thin film transistors (TFTs), and Si three-dimensional photonic bandgap crystals, and SiGe single-hole transistors.; Polysilicon films created by solid-phase crystallization of a-Si are of great interest. The low transport mobility of poly-Si TFTs relative to single-crystalline Si MOSFETs is due to scattering from grain boundaries and intragranular defects in poly-Si films. To remove grain boundaries, we used a hydrogen plasma treatment of an a-Si film through an opening hole (≤0.6 mum in diameter). Subsequent anneals at 600°C lead to a single-grain silicon film in the hole. By removing the underlying SiO2 of a-Si film, the intra-grain defect density in poly-Si was reduced by one-order of magnitude from ∼1011 cm-2 to ∼1010 cm-2. These improvements are thought to be able to improve the electrical performance of poly-Si TFTs.; Photonic crystals prohibit light propagation in a specific wavelength range. 3-D periodic face-centered-cubic structures made of SiO2 spheres by self-assembly cannot form a photonic bandgap. We used a-Si chemical vapor deposition and wet chemical etching to successfully invert the periodic structures from SiO2/air into air/Si with a relatively higher refractive index contrast. The key deposition condition is the extremely low partial pressure of SiH4 gas, which leads to a long mean free path of Si atoms and conformal growth on silica spheres. Unity reflectance occurs at a wavelength of 1.3 mum in <100> and <111> directions.; The usefulness of Si-based quantum dot devices is limited by the existence of defect states related to the SiO2 passivation, resulting in irreproducible and undesired characteristics. A new nanopatterning technique of Si/SiGe heterostructures based on the AFM local oxidation and selective wet etching has been developed to fabricate SiGe quantum dot devices. To remove the negative effects of SiO2, the surface of patterned SiGe dots was passivated by silicon epitaxial regrowth with in-situ hydrogen pre-baking at T ≤ 800°C. The regrowth interface was epitaxial, characterized by SIMS, photoluminescence, and cross-section TEM. In contrast with the unpassivated SiGe quantum dot device, the passivated SiGe single-hole transistor exhibits reproducible Coulomb blockade oscillations.